Autocabinet

I'm flabbergasted at what cabinets cost. Every house and apartment has them, for storing dishes and things, they're very simple, and they're several hundred dollars. For a very simple arrangement of wood. What the hell?
I'm imaging a system that, given six planes of particle board, slices them into a very attractive arrangement of cabinet, and staples them together. Or nails them together. Or in some way attaches the pieces. It also attaches shelves. Users take this to a forklift-like device that holds them against the wall, where users, knowing where the wall studs are, drills them into place.
Total cost: about $40.
Of course, one problem: No doors on this arrangement, and lots of scrap. But people prefer artistic doors anyway, and would probably be willing to pay a human carpenter to come up with something interesting.

Talky Tablet

It's technically possible now for you to build yourself a tablet-style computer, with a touch screen interface, and the ability to receive your voice over microphone, transcribe it to text, and place it in any application. Therefore, in theory, you could do all your computer work with your voice.
The bad news? Well, a touch-screen computer tablet is available directly right now, in the form of an I-Pad, which is super expensive. The more reasonable priced one is a kit, one you have to build yourself. Doable if you're an IT expert like me. Less so if you're some other profession and just want to take it out of the box and get to work. Also, the kit only runs Linux, and while improvements have been made over the last ten years, Linux is not exactly famous for user friendliness.
There's bad news on the speech recognition end too. It still isn't entirely sure exactly what you said. It has a pretty good idea, but after every sentence, you have to go through a touch-based entry to point out what words were said. (It shows you the most likely ones. Sometimes what you said is none of the above, and you have to get out the virtual keyboard. Those are no fun.) Still, a very advanced system. It's called Parakeet. The creators have a video of it working on a Nokia-based phone.
In theory, I could write this blog with a notepad-like device and my voice from anywhere. In practice? Keyboard at the terminal is faster.

Irish Mail

The Irish Mail is an arm powered device that you can build yourself. Like a bicycle, it uses only your own power to move you around, but is much more powerful than walking on your own two feet. Unlike a bicycle, operating an Irish Mail builds your arm muscles, especially your biceps and triceps.
Most ordering kits tend to be child-sized. Adults will want to build theirs larger, and perhaps attach a cart to the back for storing items. Both would benefit from the addition of rear-view mirrors, reflectors, and other such safety features.
Adults who replace one short drive with a car with a short trip with the irish mail can expect to lose up to 20 pounds per year. Take that, obesity.